Bill James is not familiar with tennis equipment then...
I've been clocked at 125, but there's no way I could ever throw 90+mph regularly with a baseball.
Tennis is one of the few sports where height disadvantaged individuals have somewhat of a decent chance at playing on an equal playing field with taller peeps. I'm 5"8 on a good day, and most of the guys i play with are 6"0+. Those extra few inches of height are the difference between me hitting the net on the serve, and them getting it in with more speed.
My hand is not big enough to grip a baseball as tightly as someone like Verlander or even someone like Tim Hudson. In tennis however, you can have different grip sizes for the racket handle. In addition to that, racket weight ranges anywhere from 9.5oz to 12.8z. Generally if you're in the lower margin you can't generate your own swing speed so it's light to compensate, and if it's heavier, you are strong enough to swing really fast and impart a lot of impact.
The biggest variable in modern tennis, which is why nearly every male can serve 120-140 at ease, is racket strings. It's kind of like how Bonds lead the change to maple bats, now a lot of players use it compared to ash.
Now the great thing about tennis players is, the service motion is always the same so mechanically nearly every professional/collegiate leveled serve is on the same plane mechanically. It isn't like night and day looking at Alex Wood vs. Felix Hernandez. Some have a different motion leading up to point of contact (sliding a foot, or keeping foot still mainly for timing) but the mechanics are all almost the same. And serving is closer to an outfielder throwing everything he has to home plate trying to throw out a runner, than a pitcher throwing downward off the mound. Servers do use sliders (curving slice), a topspin serve (12:6 curveball) kick serve (a 9:3 slurve, that has an insane bounce), change ups, and fastballs.
